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Smart 'stat modulation

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Need to choose one of two system boilers (Worcester 4000 or glow worm energy 7). I want modulation for all the obvious reasons. I also want smart controls so we can add smart TRVs upstairs to zone off the area. Currently not possible to zone it the manual way due to existing plumbing.

So I've come up against the issue that neither boilers are opentherm and the thermostats we like (tado or nest) don't modulate without it. Plumber has done some homework and thinks that adding weather compensation will take care of the modulation while allowing the smart controls to call for heat via relay.


Two questions to you knowledgeable folk:

1) Is my plumber right?

2) Will the call for water cylinder heating also be affected by said weather compensation? 


On point 2, the glow worm has a heat setting Dedicated to hot water if that makes a difference.


Last question:

3) Do you know of a smart thermostat system (with TRVs) that can natively modulate central heating output using the above boilers?



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Why limit yourself to those boilers.


Just get a decent combi, Atag, Intergas Viessmann. If the boiler isn't opentherm equipped as standard move on to another boiler.


You need to configure the system as priority demand hot water or X plan. Then have the heating on weather comparison and when cylinder calls for heat the boiler runs at high temperature.


The ones I mentioned above do it out the box. 


You can get a standard kit to convert any opentherm boiler to X plan.




Really do you need or just want smart controls? You want good quality trv's with remote sensing, so they measure room temp, not the temperature at the radiator. Tado do not modulate boiler unless you buy the European model, ones sold in UK trade outlets are on off only.

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Thanks. The boiler selection is based on what the plumber is supplying. I will question that as it may help like you suggest.


The smart bit is definitely a want but it will allow us to zone off the upstairs. We like a cold bedroom. I'm happy to set up remote sensing. I already have stuff in the house that will do it. Just needs setting up in home assistant.


Are you suggesting that a well set up opentherm boiler will put perform the weather compensation hack as per the plumbers suggestion?

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Not sure why you need additional relays, think you may be thinking along the wrong lines. Blasting the whole house with high temperature heat is just not efficient, to operate you need thermostats everywhere to control over and under temperature swings. Bit like driving a car with full throttle and idle only.


Weather compensation will just supply the house with enough energy to match the energy being lost to the outside world.  So the boiler runs for long periods at a low flow temperature. Efficiency gains are in the order of 20 to 30% (less gas usage). Boiler efficiency goes from 80ish to 110%.


So only use the boiler manufacturer controller for the main part of house, it will have a time schedule and different temperature profiles, and then TRVs on the bedroom rads.


Basically set the WC curve, manufacturer manual will give you a start point on that, add room compensation feature also (setting inside the controller), this will fine tune the settings based on what really happens in the house and may also optimise the start and stop timings. Set the schedule to give you temp you want and setback 2 to 3 degrees only at night. Use the trv's to get the bedroom temps where you want.


You really don't need any smart controls, let the boiler control manage it all.



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10 hours ago, MarkyG82 said:

1) Is my plumber right?


Not quite. With the Worcester controls, you'll use something like the EasyControl with the Worcester smart trvs to achieve modulation. In this instance you'll get the Easycontrol to turn the boiler on/off with modulation and just use the trvs to control room temp via flow control to rads not boiler control. As soon as you try to add multi-zoning using 230v relay on a Worcester you lose the modulation capability. IMHO the whole design of Worcester controls is pretty flawed and technical support for the controls is a bit random. You can't use Tado or Nest with a Worcester unless you're happy with relay control, which defeats the whole purpose. You'll also need the hot water diverter kit to be installed to provide priority hot water with the 4000.


With regards to Glow-worm, it's essentially a Vaillant, so you're better off considering Vaillant/Glow-worm controls as they're ebus - they're better than the Worcester, but you're stuck with what they've got.


TBH, just like @JohnMo says, there are plenty of other boiler options out there that can do a better job. ATAG are now offering 18 year warranties on boilers, so well worth a look. Even an Ideal Vogue Max will be opentherm with 12 year warranty with a max accredited installer, so can be set up PDHW with the EPH priority hot water kit and the Ideal own brand Halo Heat & System also supports PDHW (but as I've found with a couple of installs the Halo is a bit buggy and tech support doesn't fully understand it all). Otherwise Viessman is a good option too.


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  • 3 weeks later...

Hi all.  Thanks for the pointers.  We needed to make a decision quickly so I have chosen the following.  I'd appreciate your comments even if you think I've done the wrong thing.

Worcester 4000

Zoned via manifold to upstairs, downstairs and new underfloor extension

Zones controlled by EasyControl 'stats

Priority hot water (fairly sure this will run the boiler as full chat so must be timed outside heating demand)

No smart TRVs


One of the drivers for the EasyControl system was the 10 year cover when fitted alongside the boiler.  The plumber assures me this setup will have full modulation for heating.


@JohnMo understood re the requirement for smart control.  I am a big nerd and like to have as much of that stuff as possible.  As you allude to, this would work just as well once set up whether done with smarts or by a wall control.  Doing it on my phone just means I can set it up from the sofa.

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2 hours ago, MarkyG82 said:

No smart TRVs


2 hours ago, MarkyG82 said:

The plumber assures me this setup will have full modulation for heating.


Just so you know, you will not get what you're after using the EasyControl. Re how EasyControl does zoning and modulation, read this:




It only does zoning with the smart trvs.


How is your plumber going to implement Worcester PDHW with the optional diverter valve kit and zones using motorized valves? Ask him or her to explain it to you in detail before parting with your money. Get them to show you the wiring detail in the boiler installation instructions and the EasyControl instructions and the diverter kit instructions.


It's not about the wrong decision as such, it's about whether you're actually going to get what you think you're going to get.

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15 hours ago, MarkyG82 said:

They do seem to offer what we expect.


Okay, I think a little further explanation is needed here.


When you install the hot water priority kit for a WB boiler you also install a DHW cylinder sensor which signals to the boiler when it should ramp up to high output. The EasyControl is wired into the EMS low voltage connector on the boiler, which controls modulation. To make this work, you then bridge the 230v high voltage switched live connectors so on that side the boiler is seeing constant demand.


If you install motorised valves and a UFH manifold with a pump, these are wired up to the boiler using 230v so that when the motorised valve is open, it switches 230v to the boiler's 230v switched live to make it work. Now, this setup doesn't work when you have the switched live bridged as per above. On Opentherm systems, the Opentherm controllers handle the 230v switch and then send the relevant signals to the boiler low voltage Opentherm connectors and on some controllers like the EPH ones, you can connect the DHW and CH receivers together directly using 230v switching to provide priority hot water.


Now, the WB EasyControl and the WB 4000 does not have the capability to natively handle the 230v switching while also providing modulating control, which is why WB uses smart TRVs to handle zoning and modulation.


So unless WB has devised a new add-on or changed the product in the last couple of months since my last detailed conversation with WB technical department about EasyControl and zoning with zone valves, you're still not going to get what you think you'll get. By far the best way to use EasyControl is to have one zone and the PDHW optional diverter kit and you can then run weather compensation and then, if necessary add zones using the smart trvs.


With your plan, you will have a 'smart system' but that just means you can control it on your smart device, it doesn't mean intelligent modulation.


If you still don't believe me, call WB technical and ask them about 230v switching with EasyControl and modulation.


The other option, as explained above, is choose a better boiler.

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@SimonD thanks for the detailed description. We have weather compensation and priority hot water. How this is achieved I need to find out. The boiler is in now so we are very unlikely to change it. We still have the option of adding smart TRVs if that would help but I suspect not going on your description of how it works above. 

The plumber assured us that we are getting a modulating system so I am quite annoyed if we are not. It is likely to work and will be better than we had before but one of the reasons to get a new boiler was to go away from relay control with the hive thermostat. 

I will ask the plumber about the system and get his thoughts. 


Thanks again.

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Having a read in a few places with your info in mind....

Is the bridging only a requirement for priority hot? If I disable/remove that feature would it modulate as planned even with the 230v motorised valves?

We are on cheap night rate with solar diversion get much of the hot water from electric. If we remove the requirement for heating the hot water with the boiler could we get a modulating CH system?

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